Electric drive systems for machines typically include a power circuit that selectively activates a motor at a desired torque. The motor is typically connected to a wheel or other traction device that operates to propel the machine. A hybrid drive system includes a prime mover, for example, an internal combustion engine, that drives a generator. The generator produces electrical power that is used to drive the motor. When the machine is propelled, mechanical power produced by the engine is converted to electrical power at the generator. This electrical power is often processed and/or conditioned before being supplied to the motor. The motor transforms the electrical power back into mechanical power to drive the wheels and propel the vehicle.
The machine is retarded in a mode of operation during which the operator desires to decelerate the machine. To retard the machine in this mode, the power from the engine is reduced. Typical machines also include brakes and some type of retarding mechanism to decelerate and/or stop the machine. As the machine decelerates, the momentum of the machine is transferred to the motor via rotation of the wheels. The motor acts as a generator to convert the kinetic energy of the machine to electrical power that is supplied to the drive system. This electrical energy can be dissipated through wasting, storage, or other consumption by the system in order to absorb the machine's kinetic energy.
A typical electrical retarding system includes a series of resistors or other impedance devices, through which thermal energy is dissipated when electrical current passes therethrough. Due to the size of the machine components and the magnitude of the momentum retarded, large amounts of thermal energy may be dissipated through these impedance devices, which would greatly elevate their temperature. Accordingly, various solutions in the past have involved utilizing active cooling systems to reduce the temperature of these devices. Forced convection by use of a fan or blower provides one form of active cooling for impedance devices used in electric retarding systems.
Known systems using fans or blowers include an electrically driven fan that creates an airflow passing over the impendence devices to cool them by forced convection. Such motors are typically DC motors that operate at a certain DC voltage, which is supplied from the drive system. To regulate this voltage, past systems have included transformers with taps in the generator of the system, high voltage isolators, and so forth. These systems, however, are somewhat costly and deprive the drive system of useful electrical power during operation. They also tend to reduce the overall efficiency of the machine.